The invention relates to a valve operating device for the variable adjustment of the stroke of a charge exchange valve of an internal combustion engine, wherein the charge exchange valve is in active connection with a wheel rotatable about an axis of rotation, with the interposition of a transfer element, having a control path, comprising an idle stroke track and a working stroke track, in an end portion of a lever operated by a cam of a camshaft for lifting the charge exchange valve, wherein the lever associated under spring thrust with the cam on a curved path is supported at the other end along an arcuate path for variable stroke adjustment through a pivot point that is variable in position and fixable.
A valve operating device of this kind is disclosed in DE 197 08484 A1, wherein the lever has, in its end area remote from the control path, an arcuately shaped set of teeth for engagement in teeth of a control shaft which serves as an adjustment device for varying the fulcrum position associated with a particular stroke of the charge exchange valve. The pivot point of the lever is located in this case at the point of contact with the reference circles.
With this arrangement, when the cam of an adjacent camshaft acts upon the lever, it is brought about that the latter rolls in the teeth of the stationary control shaft and at the same time, in addition to a turning movement or rotatory movement with respect to the wheel of the transmission element, a translational component of movement also occurs with the circumstance of a stroke of the charge exchange valve at variance with the intended stroke.
Another, similar valve operating device is furthermore disclosed in DE 42 23 172 C1, wherein the lever that is turned by the cam of a camshaft to achieve a variable stroke—zero stroke to full stroke—is guided by a lever turned by the cam of a camshaft at its free end adjacent to linear contact with a cam serving for stroke adjustment through a slot on a pivot pin affixed to the housing. Even in this guidance method, in case of an operation of the charge exchange valve, the lever is subjected at its pivot point to a rotatory as well as linear component of movement, while the linear component of motion corresponds to the operation of a preliminary cam or a ramp, but otherwise it acts against any increase in the dynamic of the valve operation.
The invention is addressed to the problem in the generic valve operating device, to improve a lever cinematically such that it will permit a greater valve operating dynamic in a purely rotational movement or swinging movement.
This problem is solved by the invention described and claimed hereinafter by the fact that a circular track arranged on a part of the housing of the internal combustion engine serves as a slide with a radius “R” about the axis of rotation of the wheel of the transfer element of the position-variable support of the lever, while the guidance path of the lever is formed in the area of transition between the idle stroke cam and lifting cam with a ramp set for a valve clearance in the valve operating device.
With the invention the advantage is achieved that the pivot point of the lever during the lifting action for a preset valve lift forms an invariable momentary pole and thus any translational component of movement is advantageously prevented. On this basis of the invention the time required for changing the stroke of the charge exchange valve can be reduced to a substantially greater extent, and retarding of the opening and closing sections during partial strokes is largely eliminated. Furthermore, the invention provides a valve operating device of great stiffness, which is furthermore advantageous towards greater valve acceleration. Lastly, the valve operating device of the invention permits an actual zero stroke and an increase of torque by the full opening of the charge exchange valve, combined with great strength at high speeds.
In a preferred embodiment of the invention it is proposed that the lever is supported at its end remote from the control track by a wheel which can rotate about an axis, against the circular path or slide and can be fixed each time by the adjusting system such that the wheel's axis, which can be shifted under control along a path equidistant from the circular orbit, forms the lever's pivot point serving for the particular variable stroke adjustment.
In conjunction with an additional proposal, according to which the circular-path wheel of the lever is to be arranged on needle or roller bearings on a stub shaft affixed to the lever, with the momentary pole or pivot point shifting according to the invention to the axis of the circular-path wheel of the lever, the result is a valve operating device of reduced wear with substantially less friction and high accuracy of operation, while furthermore the energy required for the adjusting system is advantageously reduced.
According to an additional preferred embodiment, a wheeled idler arm supported on the side of the housing by a hydraulic valve lifter is provided, while the ramp provided to compensate for the eliminated linear movement component is designed for a substantially constant stroke speed with a maximum stroke exceeding the greatest possible valve clearance.
Additional possibilities for the configuration of the transfer element are: formation as a tappet with a wheel, or formation as a lever with a mechanically adjusted valve clearance.